Filter vials have a tubular plunger with a filter at the bottom end of the plunger. The plunger fits into a mating vial containing a fluid and things suspended in the fluid. When the plunger is inserted into the vial fluid passes through the filter and into the plunger in order to separate the fluid from particles or molecules too large to pass through the filter in the bottom of the plunger. The filtered fluid can be extracted from the plunger for further use.
The diameter and thickness of the filters can vary greatly from filter to filter and the thickness of the filter can vary greatly even across one filter. These variations make it difficult to seal the filters so all the fluid being filtered passes through the filter, and so that fluid does not wick around the peripheral edge of the filter to contaminate the filtered fluid in the plunger. Further, as fluid is forced through the filters the filters can bow or otherwise deform and allow fluid to bypass the filter as it enters the body of the plunger. Many current assemblies use ultrasonically welded assemblies. Even if the filters are ultrasonically welded to the adjacent walls of the assemblies that still leaves plasticizers that may contaminate the fluids placed in the vials during use.
Moreover, current filter vials leave a slight gap between the bottom of the plunger and the bottom of the vial, leaving a portion of the sample unfiltered and unusable for future testing or processing. While the volume of this unfiltered sample may be small in absolute terms, it may represent a sufficiently large portion of the sample that its absence can be important. There is thus a need for a filter vial that avoids the loss of fluid samples and processes more of those samples.